Hi Sadhaika,
Thanks for posting in the Apple Support Communities. From my understanding, you’re unable to use a keyboard shortcut to change the music genre in iTunes on your Mac. I’d love to share some information with you.
First, be sure you’re taking each of these steps to change the genre in iTunes or in the Music app on your Mac, depending on your macOS version:
Change song and CD info in iTunes on Mac
Change song and CD information in Music on Mac
As for your keyboard shortcut not working as expected, I recommend double-checking your keyboard shortcuts as outlined in the articles below:
Mac keyboard shortcuts
Create keyboard shortcuts for apps on Mac
If your keyboard shortcut is added but still not working as expected, try booting into safe mode, then using the shortcut again:
Use safe mode to isolate issues with your Mac
I hope this information is useful. Kind regards.